This invention relates to a method for deoiling crude lecithin and, more particularly, to a method in which the lecithin and the acetone solvent are flowed in continuous counter-current relation.
The lecithin deoiling process requires large volumes of acetone to achieve targeted oil removal. With such quantities of acetone in process, a large inventory of acetone must be maintained. Separation of the oil-bearing acetone from the deoiled lecithin and subsequent purification of the acetone is energy intensive and expensive to accomplish. The inefficiency of the historic batch-type deoiling is manifested by high solvent usage and high solvent recovery/energy costs. For example, the acetone/lecithin ratios used in current batch extraction of crude lecithin are in the range of 15:1 to 20:1. Illustrative of the prior art batch style processing is U.S. Pat. No. 3,047,597.
By the term "crude lecithin" we not only mean dry natural lecithin derived from degumming of crude soybean oil but also chemically modified lecithins such as crude lecithins which have been hydroxylated and/or acylated.
According to the invention, much lower ratios are achieved, of the order of 3:1 to 10:1 with the attendant, significant savings. This is advantageously achieved through the use of (a) an acetone pretreatment and (b) a contacting column under conditions of agitation and residence time (utilizing spaced baffles) where the two reactants are flowed in continuous, counter-current relation.
The acetone pretreatment referred to above increases flowability, i.e., reduces viscosity and facilitates break-up of solids during extraction. It is advantageous to reduce the viscosity of the crude lecithin to below about 10,000 centipoise. Although not preferred, other viscosity reducing agents may be employed such as hexane, ethanol, methyl ethyl ketone, ethyl acetate and other like esters. The alternatives can reduce viscosity but are disadvantageous because they become mixed in the extractor with the acetone, thereby resulting increased solvent recovery costs.
A search of the art revealed no pertinent teachings. One reference specifically considered was Seifen, Oele, Fette, Wachse 1971, 98(12), 359-62 (Ger.). Chemical Abstracts, Volume 77 (1972) at 60149e describes this as a countercurrent apparatus for purification of crude lecithin by extraction with ethanol. Ethanol is not a solvent used in deoiling lecithin because the recoveries are generally in the 50-70% range which is below the broad acceptable range of commercial production, viz., 70-99.9%, the general range of 90-99.9% and the currently utilized range of 94 to 99.9%. The ethanol extraction is normally employed to remove selectively the phosphatidyl-choline component so as to achieve a specific type of lecithin, and not for deoiling. Moreover, the use of countercurrent procedures in connection with soybean processing is well known--see for example, co-owned U.S. Pat. No. 3,365,440.